In recent decades, the fortuitous confluence of advances in medical and surgical capabilities, biomedical engineering, biocompatible materials development, and electronic and computer miniaturization has produced a revolution in the field of active implantable medical devices, with resultant increases in human longevity and quality of life. Examples of active implantable medical devices include artificial hearts, implantable heart monitors and defibrillators, pacemakers, neurostimulators, ventricular assist devices, and the like. One challenge associated with the use of such devices is providing a reliable source of energy to operate the device over a long period of time.
A ventricular assist device (VAD) is a medical device that partially or completely replaces the function of a damaged or failing heart. VADs typically assist the heart and do not completely take over cardiac function or require removal of the patient's heart. A particular VAD may be used to assist the patient's right ventricle (RVAD), left ventricle (LVAD), or both ventricles (BiVAD), depending on the needs of the patient. Although VADs may sometimes be intended for short term use, for example, to provide post-operative assistance to a surgically repaired heart or as a bridge while awaiting a transplant, increasingly VADs provide a long-term solution, for example, for patients suffering from congestive heart failure and for destination therapy.
The first generation VADs were approved for use in the United States by the Food and Drug Administration in 1994. A conventional VAD pump requires a percutaneous driveline, wherein a biocompatible cable extends through the patient's body to connect the VAD to a power source and system controller.
A trans-dermal driveline has many disadvantages and negative quality-of-life impacts for a patient. Moreover, due to improvements in VAD technology and the increasingly long-term use of VADs, the most common cause of complications requiring patient hospitalization and/or affecting patient mortality is no longer failure of the VAD itself Rather the most common complications result from exit site infection (ESI) associated with the percutaneous driveline. ESI can result in repeated hospitalization, increased patient pain and suffering, and significant medical expenses incurred. Even reasonable precautions to reduce the risk of ESI can interfere with the patient's quality of life. The risk of ESI largely results from the need to continuously provide power through the protective barrier provided by the patient's skin to the implanted medical device for long-term operation of the device. It would be advantageous to provide power wirelessly to an implanted medical device such as a VAD.
Prior attempts to transfer power wirelessly through a patient's skin use conventional inductive coupling techniques, e.g., coils on the inner and outer surfaces of the skin. However, conventional inductive coupling energy transfer has several drawbacks. The need for very close separation distance between the coils, and restrictions on misalignment between the transmitting and receiving coils limit the practicality of conventional inductive coupling. The proximity limitation requires that the receiving coil be implanted just under the skin and the external transmitting coil be secured in a fixed position on the skin surface. Misalignment or excessive separation between the coils may cause the transmitter to increase the power supplied to accommodate the reduced efficiency. This effect may cause skin irritation and/or thermal injury from the increase in coil temperature due to greater power transmission, which can then lead to infections.
Some of the present inventors disclose wirelessly powered speakers using magnetically coupled resonators in Patent Application Pub. No. US 2010/0081379, to Cooper et al., which is hereby incorporated by reference in its entirety.
There is a need for improved methods and systems for providing power to active implanted medical devices.